Modern motor vehicles have internal combustion engines with direct fuel injection, wherein the fuel is injected at high pressure directly into the combustion chamber or, in the case of multi-cylinder internal combustion engines, into the combustion chambers. Such direct fuel injection requires a fuel supply device which provides pressurized fuel in all operating situations. Elements of said fuel supply device include the high-pressure pump, which brings the fuel to the required pressure level, and a pressure accumulator (rail), in which the fuel is stored at high pressure and from which fuel is supplied to the injection valves.
As part of the efforts made by automobile manufacturers to further reduce the fuel consumption and emissions of motor vehicles, new vehicle functions have been developed such as, for example, the automatic start-stop function, by means of which the internal combustion engine can be automatically shut down without intervention by a motor vehicle driver and can be automatically re-started for example by the accelerator or clutch pedal being depressed, without the ignition key or the starting button having to be operated. The shutdown of the internal combustion engine is in this case performed in particular in relatively long idle phases in which the drive power of the internal combustion engine is not required. In this way, considerable fuel savings can be achieved in particular in inner-city traffic with numerous stoppages at traffic signals.
Upon the starting of an internal combustion engine with fuel injection systems, the fuel must be at an adequately high pressure. In general, the adequately high pressure upon the starting of the engine must initially be generated, both after a relatively long shutdown phase and after a short shutdown phase, by the high-pressure pump which is mechanically coupled to the engine. During a starting phase, the engine of a motor vehicle is driven, without combustion, by a starter of the motor vehicle until a setpoint injection enable pressure is reached. It is to be expected that, owing to more stringent limit values with regard to particle emissions, the setpoint injection enable pressure will be increased further in future.